Conventionally, a wakefulness maintaining apparatus for maintaining wakefulness of people is suggested. The wakefulness maintaining apparatus is suitably used for maintaining a driver of a vehicle at an appropriate waking degree for driving the vehicle.
For example, a waking degree maintaining apparatus disclosed in U.S. Pat. No. 5,311,877 (corresponding to JP-5-92039-A) estimates a waking degree of a driver at first, and estimates a reaction time Rt corresponding to the waking degree. Next, a signal output threshold frequency Ns is set and an estimated reaction time Reeg (waking degree) is calculated. When the estimated reaction time Reeg exceeds the reaction time Rt, a frequency counter N is increased. When the frequency counter N exceeds the threshold frequency Ns, it is determined that a waking state is unusual, and a waking-down signal representing a reduction in the waking degree is output. When the waking-down signal is output, a stimulus having an awakening effect such as a sound, a vibration, a smell, and the like is output to the driver for a predetermined time.
When the stimulus having the awakening effect is supplied to the driver, it is required to supply the stimulus at an appropriate time so that the driver receives the stimulus without feeling uncomfortable. When the diver is surprised by receiving the stimulus suddenly or the driver is annoyed by the stimulus, the driving operation may be disturbed.
The waking degree maintaining apparatus is only designed to output the waking-down signal when the frequency counter N exceeds the threshold frequency Ns, and is not designed to supply the stimulus so that the driver receives the stimulus without feeling uncomfortable.
Alternatively, a wakefulness maintaining apparatus for a vehicle disclosed in JP-11-310053-A supplies a smell to the driver every one minutes when a reduction degree of a driver's attention exceeds a predetermined value. Additionally, when an average of a monotonous driving operation per unit time increases, the wakefulness maintaining apparatus supplies the smell at fluctuation intervals of 1/f after 5 minutes has elapsed since the last smell is supplied.
The present wakefulness maintaining apparatus is designed to restrict an uncomfortable feeling by controlling a time of supplying the smell. However, when the waking degree reduces significantly, the wakefulness maintaining apparatus may not restrict the reduction in the waking degree sufficiently.
In general, an estimated or detected waking degree is an average of a fluctuation of the waking degree for a predetermined time. Thus, in a case where the waking degree is low until the middle of the predetermined time and the waking degree returns to a high level at the end of the predetermined time, the driver receives the stimulus with the high waking degree. In the present case, the driver may be annoyed by the stimulus and may not understand why the stimulus is supplied.
Therefore, a wakefulness maintaining apparatus that can supply stimulus without making people feel uncomfortable is required.